The ability to selectively, inducibly and reversibly target mutations to specific proteins in adult mice would be a powerful tool in the study of aging. Toward this goal, we have made a tetracycline responsive ablation of the gene for the leukemia inhibitory factor receptor (LIFR) in ES cells. This mutation has transmitted through the mouse germline and mating pairs heterozygous for the targeted mutation are now producing pups. Loss of LIFR using standard non-inducible gene targeting techniques is a perinatal lethal profoundly affecting many systems including bone (osteoporosis) and glial cell development (agliogenesis). Thus, we are now poised to address: 1. the utility of a tetracycline inducible gene ablation approach in the study of aging 2. identification of adult consequences of LIFR loss. The inducible targeting vector incorporates a complete set of tet-off elements so that a full length rat LIFR cDNA is incorporated homologously into exon 2 of the mouse LIFR effectively ablating the mouse gene with tetracycline control of the introduced rat LIFR homolog. Because rat LIFR insertion is targeted to be under appropriate control of the endogenous mouse LIFR promoter elements, expression of rat LIFR is on where murine LIFR is constitutively expressed in the absence of a tetracycline derivative, doxycycline (Dox) and silenced in the presence of Dox. Expression of rat LIFR is reactivated upon removal of Dox. Sensitivity of this system will be studied both by semi- quantitative reverse transcription polymerase chain reaction (rtPCR) to measure whole tissue alterations in LIFR levels in response to Dox in the drinking water and by utilizing a beta-galactosidase reporter gene incorporated in the targeting construct which is also switched off in the presence of Dox. Beta-galactosidase will be visualized in situ by X-gal staining to analyze localized effects of Dox administration. Effects of Dox and preliminary analysis of biological consequences of adult LIFR ablation will be assessed in bone, the central nervous system, skeletal and cardiac muscle, lung, liver, pancreas, spleen and kidney. In summary, a new technique for adult genetic manipulation will be developed and characterized that will elucidate the role in aging of the multi-functional cytokines that utilize LIFR.